1. Field of the Invention
This invention relates to composite materials and to the methods for the manufacture of such composite materials for restorative dentistry, and more particularly to composites which are useful as crown and bridge materials, either with or without an alloy substrate, as reconstructive materials, restorative materials, filling materials, inlays, onlays, laminate veneers, dental adhesives, cements, sealants and the like.
2. Brief Description of the Related Art
In recent years, materials used for dental restorations have comprised principally acrylate or methacrylate resins. Typical acrylic resinous materials are disclosed in U.S. Pat. No. 3,066,112 to Bowen, No. 3,179,623 to Bowen, No. 3,194,784 to Bowen, No. 3,751,399 to Lee et al. and No. 3,926,906 to Lee et al. Acrylic resinous materials, however, exhibit high coefficients of thermal expansion relative to the coefficient of thermal expansion for the tooth structure, and therefore these substances by themselves proved to be less than satisfactory. The disparity in thermal expansion, coupled with high shrinkage upon polymerization, results in poor marginal adaptability, and ultimately leads to secondary decay. Furthermore, the wear and abrasion characteristics and the overall physical, mechanical, and optical properties of these unfilled acrylic resinous materials was quite poor. Composite dental restorative materials containing acrylate or methacrylate resins and fillers were thus developed, the fillers generally comprising inorganic materials based on silica, silicate glass, or quartz. Particularly suitable improved inorganic filler materials include those disclosed in commonly assigned U.S. Pat. No. 4,547,531 to Waknine, and U.S. Pat. No. 4,544,359 to Waknine. These filled compositions are useful for a variety of dental treatments and restorative functions including crown and bridge materials, fillings, adhesives, sealants, luting agents or cements, denture base materials, orthodontic materials and sealants, and other dental restorative materials. Despite their suitability for their intended purposes, however, there nonetheless remains a need in the art for dental resin materials with even more advantageous physical properties.
An improved dental composite material comprises an ethylenically unsaturated resin composition; a filler composition comprising a polyhedral oligomeric silsesquioxane filler; and a curing system. These dental composite materials are useful in a variety of dental materials, treatments, and restorative functions, including crown and bridge materials, fillings, adhesives, sealants, luting agents or cements, denture base materials, orthodontic materials and sealants, and other dental restorative materials.
A new dental restorative composition comprises a polymerizable resin composition and a polyhedral oligomeric silsesquioxane (POSS) filler. POSS-filled resins typically exhibit lower mass densities and greater stiffness, and are capable of withstanding higher temperatures, as well as higher levels of ionizing radiation. In addition, POSS-filled resins are capable of wetting fibers to desirably high degrees. The use of POSS with dental resin materials, particularly the acrylate/methacrylate resins, minimizes polymerization shrinkage and increases material toughness. The nanoscale dimensionality of the POSS fillers also allows for better aesthetic properties, including easier polishability and improved transparency.
Resin compositions suitable for use with dental restorations are well known in the art, and generally comprising ethylenically unsaturated groups that are polymerizable. Especially useful are the polymerizable acrylate or methacrylate resins such as those disclosed in U.S. Pat. No. 3,066,112 to Bowen, No. 3,179,623 to Bowen, No. 3,194,784 to Bowen, No. 3,751,399 to Lee et al., No. 3,926,906 to Lee et al., and commonly assigned U.S. Pat. No. 5,276,068 and No. 5,444,104 to Waknine, all of which are incorporated herein by reference. Other suitable resin materials include, but are not limited to, various polyurethane dimethacrylates (PUDMA), diurethane dimethacrylates (DUDMA), and other monomers and oligomers known in the art. A useful monomer disclosed in U.S. Pat. No. 5,276,068 and 5,444,104 to Waknine is polycarbonate dimethacrylate (PCDMA) which is the condensation product of two parts of a hydroxyalkylmethacrylate and 1 part of a bis(chloroformate). Another advantageous resin having lower water sorption characteristics is an ethoxylated bisphenol A dimethacrylate (EBPDMA) as disclosed in U.S. Pat. No. 6,013,694. An especially important methacrylate resin is the condensation product of bisphenol A and glycidyl methacrylate, 2,2xe2x80x2-bis [4-(3-methacryloxy-2-hydroxy propoxy)-phenyl]-propane (hereinafter abbreviated xe2x80x9cBis-GMAxe2x80x9d). Included within the scope of the resin compositions herein are the resin compositions suitable for use with glass ionomer cements, including polycarboxylic acids such as homo- and copolymers of acrylic acid and/or itaconic acid.
In addition to the aforementioned resins and oligomers, the resin compositions can further include a diluent acrylate or methacrylate monomer to increase the surface wettability of the composition and/or to decrease the viscosity of the polymerization medium. Suitable diluent monomers include those known in the art such as hydroxy alkyl methacrylates, for example 2-hydroxyethyl methacrylate and 2-hydroxypropyl methacrylate; ethylene glycol methacrylates, including ethylene glycol methacrylate, diethylene glycol methacrylate, tri(ethylene glycol) dimethacrylate and tetra(ethylene glycol) dimethacrylate; and diol dimethacrylates such as 1,4-butanedioldimethacrylate, dodecanedioldimethacryalte, or 1,6-hexanedioldimethacrylate (HDDMA). Tri(ethylene glycol) dimethacrylate (TEGDMA) is particularly preferred.
The more viscous polymerizable ethylenically unsaturated resins, i.e., PUDMA, Bis-GMA, and the like are generally present in an amount greater than or equal to about 30, preferably greater than or equal to about 50 wt % of the total composition. It is generally desirable to have the polymerizable ethylenically unsaturated resins less than or equal to about 99, preferably less than or equal to about 90, more preferably less than or equal to about 80 wt % of the total composition. Diluent monomers, when present, are incorporated into the resin composition in an amount from about 1 to about 70 wt % of the total resin composition.
In addition to the above monomers and oligomers, the resin compositions also include a curing system, which typically include polymerization initiators and polymerization accelerators; ultraviolet light absorbers; antioxidants; and other additives known in the art.
Suitable polymerization initiators are those conventional initiators known in the art. For example, visible light curable compositions employ light-sensitive compounds, including but not being limited to benzil, benzoin, benzoin methyl ether, DL-camphorquinone (CQ), and benzil diketones. Either UV-activated cure or visible light-activated cure (approximately 230 to 750 nm) is acceptable. The amount of photoinitiator is selected according to the curing rate desired. A minimal catalytically effective amount is generally about 0.01 wt % of the polymerizable resin composition, and will lead to a slower cure. Faster rates of cure are achieved with amounts of catalyst in the range from greater than about 0.01 percent to about 5 wt % of the resin composition.
Alternatively, the composition may be formulated as a self-curing system. Self-curing compositions will generally contain free radical polymerization initiators such as, for example, a peroxide in amounts ranging from about 0.01 to about 1.0 wt % of the resin composition. Particularly suitable free radical initiators are lauryl peroxide, tributyl hydroperoxide and, more particularly benzoyl peroxide.
Polymerization accelerators suitable for use are the various organic tertiary amines well known in the art. In visible light curable compositions, the tertiary amines are generally acrylate derivatives such as dimethylaminoethyl methacrylate and, particularly, diethylaminoethyl methacrylate (DEAEMA) in amounts ranging from about 0.05 to about 0.5 wt % of the resin composition. In the self-curing compositions, the tertiary amines are generally aromatic tertiary amines, preferably tertiary aromatic amines such as ethyl 4-(dimethylamino)benzoate (commonly known as xe2x80x9cEDMABxe2x80x9d), 2-[4-(dimethylamino)phenyl] ethanol, N, N-dimethyl-p-toluidine (commonly abbreviated xe2x80x9cDMPTxe2x80x9d), bis(hydroxyethyl)-p-toluidine, and triethanolamine. Such accelerators are generally present in the range from about 0.5 to about 4.0 wt % of the resin composition.
It is furthermore preferred to employ an ultraviolet absorber in amounts ranging from about 0.05 to about 5.0 wt % of the total composition. Such UV absorbers are particularly desirable in the visible light curable compositions in order to avoid discoloration of the resin from any incident ultraviolet light. Suitable UV absorbers are the various benzophenones, particularly Uv-5411 available from American Cyanamid Company.
The filler composition comprises at least one polyhedral oligomeric silsesquioxane (POSS) of the generic formula (RSiO1.5)n, wherein R is a hydrocarbon and n is 6, 8, 10, 12, or higher. These molecules have rigid, thermally stable silicon-oxygen frameworks with an oxygen to silicon ratio of 1.5, and covalently-bound hydrocarbon groups that provide an organic outer layer comprising, for example, phenyl, isooctyl, cyclohexyl, cyclopentyl, isobutyl, or other groups. Such silsesquioxanes include, for example, dodecaphenyl-POSS, octaisooctyl-POSS, octacyclohexyl-POSS, octacyclopentyl-POSS, octaisobutyl-POSS and the like. POSS typically have surface areas greater than 400 square meters per gram (m2/gm).
Functionalized POSS (also known as xe2x80x9cPOSS monomersxe2x80x9d) are particularly preferred, wherein one, two, or more of the covalently bound organic groups are reactive with at least one component of the resin composition. In some cases, it is possible to have all of the covalently bound organic groups be reactive groups. POSS monomers may be prepared, for example, by corner-capping an incompletely condensed POSS containing trisilanol groups with a substituted trichlorosilane. For example, the trisilanol functionality of R7T4D3(OH)3 (wherein R is a hydrocarbon group) can be reacted with Cl3Si-Y to produce the fully condensed POSS monomer R7T8Y. Through variation of the Y group on the silane, a variety of functional groups can be placed off the corner of the POSS framework, including but not limited to halide, alcohol, amine, isocyanate, acid, acid chloride, silanols, silane, acrylate, methacrylate, olefin, and epoxide.
Preferred functional groups are acrylate (xe2x80x94Xxe2x80x94OC(O)CHxe2x95x90CH2) and methacrylate (xe2x80x94Xxe2x80x94OC(O)CH(CH3)xe2x95x90CH2) groups, wherein X is a divalent linking group having 1 to about 36 carbons, such as methylene, ethylene, propylene, isopropylene, butylene, isobutylene, phenylene, and the like. X may also be substituted with functional groups such as ether (e.g., xe2x80x94CH2CH2OCH2CH2xe2x80x94), as long as such functional groups do not interfere with formation or use of the POSS. X is preferably propylene, isobutylene, or xe2x80x94OSi(CH3)2CH2CH2CH2xe2x80x94. One, all, or an intermediate number of the covalently bound groups may be acrylate or methacrylate groups. Such functionalized POSS are available from Gelest, Inc. (Tullytown, Pa.) and Hybrid Plastics. A methacryloxypropyl-substituted T8 POSS (wherein all positions of the polyhedron are methacryloxypropyl-substituted) is available under the trade designation MA0735 from Hybrid Plastics Corp.). Another methacryloxypropyl-substituted T8 POSS (wherein one position is methacryloxypropyl-substituted and the remaining positions are isobutyl-substituted) is available under the trade designation MA0702 from Hybrid Plastics Corp (Fountain Valley, Calif.).
Of course, the linking groups X are also suitable for use with other functional groups. Other POSS fillers include, for example T6, T8, T10, or T12 structures functionalized with alkoxysilanes such as diethoxymethylsilylethyl, diethoxymethylsilylpropyl, ethoxydimethylsilylethyl, ethoxydimethylsilylpropyl, triethoxysilylethyl, and the like; with styrene, such as styrenyl (C6H5CHxe2x95x90CHxe2x80x94), styryl (xe2x80x94C6H4CHxe2x95x90CH2) and the like; with olefins such as allyl, xe2x80x94OSi(CH3)2CH2CH2xe2x95x90CH2, cyclohexenylethyl, xe2x80x94OSi(CH3)2CHxe2x95x90CH2 and the like; with epoxies, such as 4-propyl-1,2-epoxycyclohexyl, 3-propoxy, glycidyl (xe2x80x94CH2CH2CH2OCH2CH(O)CH2), and the like; with chlorosilanes such as chlorosilylethyl, dichlorosilylethyl, trichlorosilylethyl, and the like; with amines such as aminopropyl, aminoethylaminopropyl, and the like; with alcohols and phenols such as xe2x80x94OSi(CH3)2CH2CH2CH2OC(CH2CH3)2(CH2CH2OH), 4-propylene-trans-1,2-cyclohexanediol, xe2x80x94CH2CH2CH2OCH2C(CH2OH)(OH), and the like; with phosphines such as diphenylphosphinoethyl, diphenylphosphinopropyl, and the like; with norbomenyls such as norbomenylethyl; with nitrites such as cyanoethyl, cyanopropyl, xe2x80x94OSi(CH3)2CH2CH2CH2CN, and the like; with isocyanates such as isocyanatopropyl, xe2x80x94OSi(CH3)2CH2CH2CH2NCO, and the like, with halides such as 3-chloropropyl, chlorobenzyl (xe2x80x94C6H4CH2Cl), chlorobenzylethyl, 4-chlorophenyl, trifluoropropyl (including a T8 cube with eight trifluoropropyl substitutions) and the like; and with esters, such as ethyl undecanoat-1-yl and methyl propionat-1-yl, and the like. Certain polymers such as poly(dimethyl-comethylhydrido-co-methylpropyl polymers, poly(dimethyl-comethylvinyl-co-methylethylsiloxy, poly(ethylnorbonenyl-co-norbonene) and poly(ethylsilsesquioxan) may also be used to functionalize POSS. Many of these substitutions are commercially available on T8 POSS from Hybrid Plastics.
Without being bound by theory, it is hypothesized that the functionalization of the cubes allow for better dispersion in and reactivity with the matrix resin, which reduces moisture uptake, as well as volumetric shrinkage. Bonding of the T8 cubes with the matrix resin may be achieved by co-polymerization with the resin monomers or oligomers in the presence of a cure system, for example by treatment with radiation such as UV light.
In addition to the POSS-based filler, the filler composition may further comprise one or more of the inorganic fillers currently used in dental restorative materials. Preferred additional fillers include those that are capable of being covalently bonded to the resin matrix itself or to a coupling agent that is covalently bonded to both. Examples of suitable filling materials include but are not limited to, silica, quartz, strontium silicate, strontium borosilicate, lithium silicate, lithium alumina silicate, amorphous silica, ammoniated or deammoniated calcium phosphate, tricalcium phosphate alumina, zirconia, tin oxide, and titania. Some of the aforementioned inorganic filling materials and methods of preparation thereof are disclosed in U.S. Pat. No. 4,544,359 and No. 4,547,531, pertinent portions of which are incorporated herein by reference. Suitable high refractive index filler materials such as high refractive index silica glass fillers and calcium silicate based fillers such as apatites, hydroxyapatites or modified hydroxyapatite compositions may also be used. Alternatively, inert, non-toxic radiopaque materials such as bismuth oxide (Bi2O3), barium sulfate, and bismuth subcarbonate may be used. Suitable fillers have a particle size in the range from about 0.1 to about 5.0 microns, and may further comprise unbound silicate colloids of about 0.001 to about 0.07 microns. These additional fillers may also be silanized.
The amount of total filler composition in the dental composite can vary widely, being in the range from about 1 to about 90 wt % of the total composition. The amount used is determined by the requirements of the particular application. Thus, for example, crown and bridge materials generally comprise from about 60 to about 90 wt % filler; luting cements comprise from about 20 to about 80 wt % filler; sealants generally comprise from about 1 to about 20 wt % filler; adhesives generally comprise from about 1 to about 30 wt % filler; and restorative materials comprise from about 50 to about 90 wt % filler, with the remainder in all cases being the resin composition and curing system.
The amount of POSS in the filler composition relative to other filler may also vary widely, depending on the requirements of the particular application. The POSS may accordingly comprise from less than about 1 to 100 wt % of the total filler composition, preferably from about 1 to about 100 wt % of the total filler composition for sealers and adhesives, and from about 2 to about 30 wt % of the total filler composition for crown and bridge materials and dental restorative materials.
In a preferred embodiment, in one manner of proceeding the polymerizable resin composition (including any desired diluent monomers), the POSS filler, and any additional fillers are mixed. The curing system is added to the mixture, which is again stirred and stored or used, as appropriate. The cure may be initiated through the use of UV light or by raising the temperature of the mixture. The dental restorative resin thus obtained is then placed in the tooth to be repaired after it is appropriately prepared. Methods for use of the above-described compositions are well known in the art. The invention is further illustrated by the following non-limiting examples.